Men can't pack a bag.

Men wouldn't be caught dead wearing red velvet.

Men would feel their masculinity is threatened... having to be seen with all those elves.

Men don't answer their mail.

Men would refuse to allow their physique to be described, even in jest, as anything remotely resembling a "bowlful of jelly."

Men aren't interested in stockings unless somebody's wearing them.

Having to do the "Ho, Ho, Ho," thing would seriously inhibit their ability to pick up women.

Finally, being responsible for Christmas would require a commitment.